Hubble Gets Best Look Yet At Messier 9

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First discovered by Charles Messier in 1764, the globular cluster Messier 9 is a vast swarm of ancient stars located 25,000 light-years away, close to the center of the galaxy. Too distant to be seen with the naked eye, the cluster’s innermost stars have never been individually resolved… until now.

This image from the Hubble Space Telescope is the most detailed view yet into Messier 9, capturing details of over 250,000 stars within it. Stars’ shape, size and color can be determined — giving astronomers more clues as to what the cluster’s stars are made of. (Download a large 10 mb JPEG file here.)

Hot blue stars as well as cooler red stars can be seen in Messier 9, along with more Sun-like yellow stars.

Unlike our Sun, however, Messier 9’s stars are nearly ten billion years old — twice the Sun’s age — and are made up of much less heavy elements.

Since heavy elements (such as carbon, oxygen and iron) are formed inside the cores of stars and dispersed into the galaxy when the stars eventually go supernova, stars that formed early on were birthed from clouds of material that weren’t yet rich in such elements.

Zoom into the Messier 9 cluster with a video from NASA and the European Space Agency below:

The Hubble Space Telescope is a project of international cooperation between ESA and NASA. See more at www.spacetelescope.org.

Most of the blue stars are subdwarfs near the end of mainsequence, and are soon(tm) about to swell up to red giants. They still fuse hydrogen into helium in the core.
The red giants are those stars that are just a little more evolved than the blue ones, because they are a little heavier. These have stopped fusing hydrogen, and some have started to fuse helium into carbon wich gives them a significant luminosity boost..

Some of the blue stars are also something called “blue stragglers”, stars that seem to be the result of mergers or collisions of 2 or more stars.

Stars significantly heavier than the ones we see are long gone, and now remain as white dwarfs or neutron stars.

The exact distance from the Sun to the Galactic Center is notoriously uncertain. The latest estimates from geometric-based methods and standard candles yield distances to the Galactic Center between 7.6-8.7 kpc (25,000-28,000 light years). The fact that the estimates span over 1 kpc (3262 ly) only underscores the true uncertainty associated with the distance to the Galactic center. [from http://en.wikipedia.org/wiki/Galactic_Center ]